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Bad News About Monarch Butterflies in California and Elsewhere

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This month in Pismo Beach | Photo: Castles, capes and clones/Flickr/Creative Commons License

North America's monarch butterflies are in trouble, a sad fact that's making the news this week. Habitat destruction seems to be the main cause, with Midwestern farmers' eradication of the milkweed the emblematic butterflies need to reproduce fingered by scientists as a main reason for the decline.

That means more than just a drop in the numbers of the dramatically colored butterfly: it also means a possible end to one of the continent's most impressive natural spectacles: the annual migration of millions of monarchs between Canada, the U.S. and Mexico.

And the problem isn't limited to the Midwest. According to a fifteen-year study of western monarch numbers by a leading butterfly conservation group, the monarch's numbers are crashing in California as well.

The monarch butterfly, Danaus plexippus, may well be the most popular insect in North America. For years, the spectacle of the orange and black butterflies gathering by the millions has attracted admirers to wintering grounds in Central Mexico, and summer gathering spots along the California coast.

As the annual migration takes longer than the usual lifespan of a monarch adult, the butterflies must breed along the way. That means that migrating butterflies must find stands of milkweed plants, any of a number of species of the genus Asclepias that are the only plants their larvae can eat. If there isn't enough milkweed, the butterflies can't replenish their numbers and the migration thins.

In a joint press conference Wednesday, representatives of the Mexican Government and the World Wildlife Fund reported that only half as many monarchs arrived this year as last year at their overwintering area in the Mexican Sierra Madre. (That's the winter destination for monarchs from east of the Rocky Mountains.) By comparison, in 1996 more than 25 times as many monarchs found their way to the Sierra Madre as did this winter.

The drop from last year is likely due at least in part to bad weather. But the much more dramatic long-term drop in numbers is likely the result of near-eradication of milkweed from much of the Great Plains.

The decline in Great Plains milkweed can be laid at the feet of agriculture. Subsidies for ethanol production have prompted the conversion of vast areas of monarch milkweed habitat to cornfields. Some critics are pointing an accusing finger at GMO crops as well, saying that herbicide-resistant food crops promote the use of weed-killers that kill milkweed. (Which would mean it's the herbicide rather than the GMO doing the damage, but that may be a fine point.)

But it's not just eastern monarchs that are declining. According to the invertebrate conservation group the Xerces Society, California's migrating monarch butterflies may have declined in number by as much as 90 percent between 1997 and 2012.

The Xerces Society, named in 1971 after a species of California butterfly driven to extinction by development in California, has conducted an annual Thanksgiving monarch butterfly count since 1997 at about 100 locations in California, as well as another dozen or so in Baja California and Arizona.

Though the stats for the 2013 count are still being compiled, the figures for '97 through 2012 are sobering. In 1997, Xerces' volunteer counters recorded an estimated 1,235,490 monarchs at 101 sites in California and Baja. By 2012, that number had dropped to 144,650, less than 12 percent of the 1997 count, despite the fact that 2012's count covered an additional 19 sites.

At nearly all of the count sites listed numbers dropped precipitously after 1997, with places that had once hosted thousands of visiting monarchs subsequently seeing a few hundred, and sometimes none.

Some locations have informally reported that their 2013 monarch count numbers were up compared to 2012, but even if that holds true across the state, the long-term trends are still troubling.

California's milkweeds are just as susceptible to being sprayed and plowed under as their midwestern relatives, but they also have drought, fire, and spreading urban development to contend with. When hillsides are too dry for milkweed seeds to germinate, or when whole swathes of grassland burn down, the butterflies go without food for their caterpillars.

This is one of those wildlife depletion issues where individual Californians can make a difference, by planting milkweeds in their gardens. Some California native milkweeds are even showy, and the site Monarch Watch offers a list of potential sources.

Planting a bit of a butterfly garden might seem like a small thing, but at this point the monarchs need every little bit of help they can get.

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